This invention relates to the driving mechanism of a mechanical seal face, especially where the seal face is a soft or brittle material and its drive contact gets damage in respect of high pressure and rotation.
A mechanical seal comprises a xe2x80x9cfloatingxe2x80x9d component which is mounted axially movably around the rotary shaft of, for example a pump and a xe2x80x9cstaticxe2x80x9d component which is axially fixed, typically being secured to a housing. The floating component has a flat annular end face, i.e. its seal face, directed towards a complementary seal face of the static component. The floating component is urged towards the static component to close the seal faces together to form a sliding face seal, usually by means of one or more springs. In use, one of the floating and static components rotates; this component is therefore referred to as the rotary component. The other of the floating and static components does not rotate and is referred to as the stationary component.
Those seals whose floating component is rotary are described as rotary seals. If the floating component is stationary, the seal is referred to as a stationary seal.
If the sliding seal between the rotary and stationary components are assembled and pre-set prior to despatch from the mechanical seal manufacturing premises, the industry terminology for this is xe2x80x9ccartridge sealxe2x80x9d. If however the rotary and stationary components are despatched individually (unassembled) from the mechanical seal manufacturing premises, the industry terminology for this is xe2x80x9ccomponent sealxe2x80x9d.
Seal faces are generally held to their relevant stationary or rotary components by a mechanism that is called drive ring. One of the common mechanisms is the use of slots on the back of seal face and lugs on the drive ring or vice versa. FIG. 1 shows four slots on the seal face and four lugs on the drive ring. FIG. 2 shows two lugs on the seal face and two lugs on the drive ring. Rotation will be transferred from the seal faces to the drive ring at rotary faces or vice versa at the stationary faces.
Seal faces are mainly supplied from various grades of silicon carbide, tungsten carbide, ceramics and carbon. Carbon is categorised as a soft face.
The contact between the slots and lugs in FIGS. 1 and 2 is mainly point contact. Under point contact, soft or brittle seal faces are more prone to failure than hard faces, especially in high pressure and large seal size applications. The failure may start by notch propagation around the contact point which gradually grows until it destroys the seal face.
Instead of having lugs on the drive ring, some designs employ drive pins that are pressed firmly into holes in the drive ring. These pins cannot move or rotate from their location. FIG. 3-2 illustrates the use of two pins to drive a lug on the seal face when the seal rotates either in clockwise or counter-clockwise direction. If the mechanical seal is designed to only rotate in one direction, one pin can be used for each lug. Alternatively, the pin may be square, cylindrical or any other shape (See FIGS. 4-a and 4-b).
The drive ring may also be designed to drive the seal face around the outer diameter, inner diameter or axial end of said face. This is shown in FIG. 4 where point contacts between the lug and slot are labelled A and B.
The invention relates to a floating pin that allows the interface between the lug and the slot to be a line or face contact. Preferably the pin is of circular shank diameter, preferably with a square or rectangular head and is loosely fitted in a hole to allow free rotation of said pin about its axis.